At present, fluid materials such as liquid, mixtures of different liquids, mixtures of liquids and solids or gases, colloids, or gels are increasingly used as thermal media in numerous heating and/or cooling systems. In general, heat transfer characteristics, for example, thermal conductivity, of the fluid materials are physical properties which can be used to evaluate thermal efficiencies of the heating and/or cooling systems. The heat transfer characteristics of the fluid materials largely depend on their composition, mixing condition of ingredients and other factors, and are difficult to predict from the properties of their additives. Thus, measurement of the heat transfer characteristics is essential for using the fluid materials.
Many devices for measuring the heat transfer characteristics of the fluid materials typically use various types of detectors including a Wheatstone bridge with a metal filament coupled to one leg of the Wheatstone bridge. The metal filament is placed in a cavity through which the sample to be measured is passed. The practical implementation of such apparatuses, however, has encountered serious problems, such as drift in the voltage that controls current in the metal filament and serious inaccuracies in the results when even small variations occur in the temperature of the sample or in the temperature of the cavity. In order to ensure accuracy and credibility, the metal filament needs to be replaced frequently, but metal filaments can be very expensive because of the requirement for low reactivity and linearity of the voltage-temperature response.
Some devices are used for measuring the heat transfer characteristics of colloid by fastening a colloid between a heating block and a cooling block at a predetermined pressure. The two blocks each define a number of orifices each receiving a thermal probe therein, for measuring temperature of the respective locations in the block where each thermal probe is positioned. Generally, the predetermined pressure is maintained at a constant level during measurement in order to ensure constant contact between the colloid and the two blocks. Thus, based on the predetermined pressure, the thermal resistance and the thermal conductivity of the colloid can be respectively calculated from the equations (1) and (2) as follows:
                              R          =                                    (                                                T                  1                                -                                  T                  2                                            )                        Q                          ,                            (        1        )                                          K          =                                    Q              ×              L                                      A              ×                              (                                                      T                    1                                    -                                      T                    2                                                  )                                                    ,                            (        2        )            Accordingly, a relationship equation (3) between the thermal resistance and the thermal conductivity can be deduced from the two equations (1) and (2) above as follows:
                              R          =                      L                          A              ×              K                                      ,                            (        3        )            wherein R is thermal resistance between the two blocks; T1 and T2 are interface temperatures of the heating block and the cooling block respectively, Q is heat flux transferred to the colloid, L is heat transfer distance (i.e. thickness) of the colloid, A is cross sectional area in the heat transfer direction, and K is thermal conductivity of the colloid.
In the equations above, T1 and T2 can be detected via the thermal probes, Q can be obtained via the output power of the heating block, L and A can be directly obtained from the thickness and the cross sectional area of the colloid. As such, the R and K can be calculated from the equations above. Nevertheless, the colloid is prone to seep out of the interspace defined by the two blocks. This can result in an inaccurate determination of the thicknesses of the colloid.
In order to overcome shortcomings set out above, a gasket is applied between the two blocks for preventing the colloid from seeping out of the interspace defined by the two blocks. However, the gasket creates uneven pressure over the surfaces fastening the colloid so that contact status of the colloid with the two blocks can be inaccurately determined. That is, the gasket can make actual heat transfer characteristics difficult to measure.
What is needed, therefore, is a device for measuring heat transfer characteristics of a fluid material with relatively high accuracy.
What is also needed, therefore, is a method for measuring heat transfer characteristics of a fluid material.